Engines may use a turbocharger to improve engine torque/power output density. In one example, a turbocharger may include a compressor and a turbine connected by a drive shaft, where the turbine is coupled to the exhaust manifold side and the compressor is coupled to the intake manifold side. In this way, the exhaust-driven turbine supplies energy to the compressor to increase the pressure in the intake manifold (e.g. boost, or boost pressure) and to increase the flow of air into the engine. The boost may be controlled by adjusting the amount of gas reaching the turbine, such as with a wastegate.
In one example, the wastegate may include a first port coupled to boost pressure, a second port coupled to atmospheric pressure, and a valve configured to control the flow of exhaust gasses according to the wastegate duty cycle. This configuration may be referred to as a “boost-based” configuration because the force to actuate the wastegate valve comes from the boost pressure. For example, a solenoid valve may connect a wastegate canister chamber having a wastegate canister pressure to the first port coupled to boost pressure and the second port coupled to atmospheric pressure. When the solenoid valve is in a first position, the first port and the wastegate canister chamber are in communication and the wastegate canister pressure will increase toward boost pressure. When the solenoid valve is in a second position, the second port and the wastegate canister chamber are in communication and the wastegate canister pressure will decrease toward atmospheric pressure. By moving the solenoid valve from the first position to the second position via the wastegate (solenoid) duty cycle, the wastegate canister pressure may be maintained at a value between the boost pressure and the atmospheric pressure. The wastegate canister pressure may be used to actuate the wastegate valve and thus control the boost pressure. Thus, the position of the wastegate valve may be determined by the boost pressure, atmospheric pressure, and the wastegate duty cycle.
The inventors herein have recognized that the wastegate is used to control the boost pressure, and the boost pressure relative to atmospheric pressure provides the motive force for moving the wastegate. For example, the atmospheric pressure may change with altitude or weather conditions which may affect the pressure difference between boost and atmospheric pressure, and hence the ability to control the boost pressure. Additionally, a circular interaction of controlling the boost pressure with the wastegate and actuating the wastegate with the boost pressure makes the wastegate operation less predictable than desired. One approach to address the above issues is a method that includes actuating the wastegate with boost pressure generated by the turbocharger. The wastegate is adjusted according to a difference between the boost pressure and the atmospheric pressure. In this way, the interdependency between controlling the boost pressure and using the boost pressure to actuate a boost-based wastegate is reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.